The interior spaces of structures exposed to extreme heat and cold are typically heated and cooled by active systems, such as furnaces and air conditioners. Unfortunately, such temperature regulating systems demand a substantial amount of electric or other type of external power which generates large operating costs in addition to the initial cost of the system. Of course, the cost of active temperature regulating systems is not always prohibitive in structures designed for human habitation or use, such as homes, office buildings, factories and the like. However, temperature regulating systems are often desirable in other types of structures where the installation and operating costs of active systems cannot be justified, such as relatively small or remote structures designed to house livestock or electrical or fiber-optic equipment. It is often not feasible to bring electricity to a remote structure or to provide for the generation of electricity on-site, or to provide an alternative source of power. As a result, active systems often cannot be used in situations in which some form of temperature control is highly desirable.
In an attempt to solve some of the above problems, passive cooling systems have been developed to provide cooling by passively radiating heat to the night air and sky. One such system is disclosed in commonly assigned U.S. Pat. No. 5,070,933 to Baer, the complete disclosure of which is incorporated herein by reference. In this cooling system, a plurality of plastic containers filled with water and insulation are mounted to the roof of the structure. The insulation contains vertical passages so that the water may flow between the top and bottom of the container. During the evening, relatively cold water, chilled by the night air and sky radiation, flows downwardly through the vertical passages in the insulation to the body of the container and cools the interior of the structure by heat transfer. During the day, the flow of water ceases, and insulation and standing water minimize the penetration of heat from the outside.
One problem with existing passive cooling systems such as the above referenced patent is that the plastic containers filled with water and insulation are heavy. Therefore, these systems typically include a large and relatively expensive support system to hold the plastic containers against the roof of the structure. In addition, gravity and thermal stresses eventually cause the heavy plastic containers to sag away from the roof of the structure. This decreases the heat transfer from the water to the cool night air and night sky because the plastic containers are no longer in intimate contact with the roof.
The above problems with supporting plastic containers against a roof have been addressed by another passive cooling system disclosed in commonly assigned U.S. patent application Ser. No. 08/277,925 to Harrison, the complete disclosure of which is incorporated herein by reference. In this system, plastic containers are integrally formed to the roof of the structure by melting plastic in a lower mold portion removably attached to an upper wall section (i.e., a portion of the roof). After cooling, the lower mold portion is removed and the cooled plastic forms a container which is an integral part of the upper wall section or roof. Although the containers in this cooling system generally remain in contact with the roof during use, they are typically expensive to manufacture. This is because the containers must be rotationally molded so that they will be integral with the surface of the upper wall or roof section.
Other passive cooling systems have been disclosed in U.S. Pat. Nos. 3,563,305 and 4,089,916 to Hay and U.S. Pat. No. 4,615,381 to Malloney. The Hay patents generally describe systems having water containers or ponds horizontally disposed atop the enclosure in direct thermal exchange with the underlying space by thermosiphon action. Malloney discloses a system comprising tanks of water that are integrally attached to the roof of the structure. These systems, however, are limited because they are an integral, permanent part of the structure's outer wall or roof. Therefore, the entire outer wall or roof must be specially designed to incorporate the cooling system. In addition, since these prior art systems are integral with the outer walls or roof, they generally cannot be removed without also removing (and possibly destroying) the roof or outer walls of the structure.